It sounds like science fiction: We can build machines that take carbon dioxide out of the atmosphere, thus averting potentially dire impacts from climate change. As we discussed last week though, it’s true. In fact, we’re depending on this type of approach, known as novel CDR, or carbon dioxide removal, to ramp up drastically in the coming years.

This week, we’ll look at two other parts of this conversation that also sound like keen fabrications of sci-fi world-building. Neither is technically carbon dioxide removal, and neither is a climate fix you’d do well to bet the planet on, but both are worth knowing about the next time solutions like CDR come up at a party. They both also go by a few different names.

First, there’s carbon capture and storage (CCS) or carbon capture and utilization (CCU). The convenient shorthand we’ll use for both is CCUS. Then there’s solar geoengineering, also sometimes known as SRM, which stands for solar radiation modification or management. Phew, enough wonky terms.

CCUS

CCUS means capturing carbon dioxide at its source—an industrial smokestack, let’s say—and then either storing it or turning it into a product. It generally doesn’t tick all the boxes to fit the IPCC’s definition of CDR because it’s usually not capturing CO₂ from the atmosphere at large, plus any products created would have to store the involved carbon for a “climate-relevant time horizon.” 

CCUS has been around since the 1970s. Pioneered in Texas by Occidental, the earliest form directed intense flows of CO₂ into oil wells for “enhanced oil recovery.” It hasn’t exactly morphed into a top-flight climate solution in the decades since.

“For many years, oil and gas companies have been touting CCS as a one-stop solution to abate emissions from fossil fuel extraction and utilisation,” says a report out this month from Climate Tracker, which “ found a consistent trend of over-promising and under-delivering.”

There are about 40 CCUS projects in the world, mostly in the US, representing the potential to capture about 0.1 percent of global CO₂ emissions, the report says. And a lot of what is captured is still used for enhanced oil recovery, which, in a world that needs to quit burning fossil fuels, is not what you want.

While it was once reasonable to ask if CCUS could help abate emissions from hard-to-decarbonize industries like concrete and steel, the report throws cold water on that hope. Despite decades and many billions of dollars, CCUS still tends to require custom engineering that isn’t modular, and it shows little promise of getting much cheaper or easier to scale the way renewables and batteries have. 

Geoengineering

Let’s turn now to another idea that comes up when talk turns to tinkering with the planet.

You probably already know the core problem of global heating is that burning fossil fuels emits greenhouse gases that trap energy from the sun, making our planet hotter. Most efforts to solve this problem center on our need to stop burning fossil fuels; there is no substitute for this. CDR complements this work by attempting to take some heat-trapping CO₂ out of the atmosphere.

Now enter solar geoengineering, which asks, “Hey guys, what if I just reflect some of that energy from the sun back into space in the first place?” One way you could do this, perhaps for just a few billion dollars, is by spraying sulfate aerosols into the upper atmosphere, where they’ll remain for a few years. 

We’ve already experienced a version of this process from time to time by way of volcanic eruptions, journalist Elizabeth Kolbert observes in her 2021 book Under a White Sky: “The result is low temperatures, fantastic sunsets, and, on occasion, famine.”

Indeed, a future reliant on solar geoengineering could easily veer from sci-fi to dystopian, because the planetary side effects could be devastating, altering everything from weather patterns to the basic photosynthesis that allows us to grow food. And if we were to give spraying those aerosols a rest, the hangover, or “termination shock,” would be disastrous, as global temperatures would rapidly spike.

Calling it a “desperate” idea, The End of Nature author Bill McKibben wrote in 2022, “Everyone studying solar geoengineering seems to agree that it’s a terrible thing.”

You'd be forgiven for wondering if one day we might have to try it anyway, but we're not there yet. Whether we end up there hinges chiefly on how quickly we can scale up the means to ditch fossil fuels.